Problem: $ F = \left[\begin{array}{rr}3 & 1 \\ -2 & 4\end{array}\right]$ $ B = \left[\begin{array}{rr}-1 & 2 \\ -1 & -2\end{array}\right]$ Is $ F+ B$ defined?
Solution: In order for addition of two matrices to be defined, the matrices must have the same dimensions. If $ F$ is of dimension $( m \times  n)$ and $ B$ is of dimension $( p \times  q)$ , then for their sum to be defined: 1. $ m$ (number of rows in $ F$ ) must equal $ p$ (number of rows in $ B$ ) and 2. $ n$ (number of columns in $ F$ ) must equal $ q$ (number of columns in $ B$ Do $ F$ and $ B$ have the same number of rows? Yes Yes No Yes Do $ F$ and $ B$ have the same number of columns? Yes Yes No Yes Since $ F$ has the same dimensions $(2\times2)$ as $ B$ $(2\times2)$, $ F+ B$ is defined.